Angle-Of-Attack Flight Computer Systems and Methods

ABSTRACT

According to one implementation of the present disclosure, a method for determining angle-of-attack for an unpowered vehicle is disclosed. The method includes: determining a monotonic portion of a look-up curve of an angle-of-attack operating plot; during flight, determining, by an accelerometer disposed on the unpowered vehicle, first and second accelerometer outputs, where the first and second accelerometer outputs correspond to first and second body-fixed load factor measurements, respectively; determining an operating point on the monotonic portion by applying a quotient of the first and second accelerometer outputs to the angle-of-attack operating plot; and determining an angle-of-attack parameter corresponding to the determined operating point.

BACKGROUND

This section is intended to provide background information to facilitatea better understanding of various technologies described herein. As thesection's title implies, this is a discussion of related art. That suchart is related in no way implies that it is prior art. The related artmay or may not be prior art. It should therefore be understood that thestatements in this section are to be read in this light, and not asadmissions of prior art.

In aerospace applications, aerodynamic angle-of-attack of a vehiclerelative to the local airstream may be required for optimal performanceof a small vehicle (such as a glider). For such small vehicles, accurateestimation or measuring of angle-of-attack can be difficult to ascertaindue to the size of the required probe with respect to the size of thevehicle or the weight and expense of obtaining the inertial measurementsnecessary for accurate estimation.

Current methods to determine angle-of-attack include direct measurement(vane, cone, or pressure(s) probe), estimation based on fusion ofinertial and airspeed measurements (precise inertial measurements andaccurate airspeed measurement via a pitot-static system), and tablelookup versus aerodynamic normal force coefficient (that also requiresaccurate airspeed measurement via a pitot-static-system). However, allof these methods require the use of external probes, and the inclusionof an external probe may be prohibitively expensive and/or may not bepossible due to size, weight, or expense restrictions of the vehicle.

SUMMARY

According to one implementation of the present disclosure, a method fordetermining angle-of-attack for an unpowered vehicle is disclosed. Themethod includes: determining a monotonic portion of a look-up curve ofan angle-of-attack operating plot; during flight, determining, by anaccelerometer disposed on the unpowered vehicle, first and secondaccelerometer outputs, where the first and second accelerometer outputscorrespond to first and second body-fixed load factor measurements,respectively; determining an operating point on the monotonic portion byapplying a quotient of the first and second accelerometer outputs to theangle-of-attack operating plot; and determining an angle-of-attackparameter corresponding to the determined operating point.

According to another implementation of the present disclosure, a flightcomputer system (i.e., computer, flight control system) is disclosed.The flight control system includes a processor and a memory accessibleto the processor. The memory stores instructions that are executable bythe processor to perform operations including determining a monotonicportion of a look-up curve of an angle-of-attack operating plot; duringflight, receiving from an accelerometer disposed on the unpoweredvehicle, first and second accelerometer outputs, where the first andsecond accelerometer outputs correspond to body-fixed load factormeasurements, respectively; determining an operating point on themonotonic portion by applying a quotient of the first and secondaccelerometer outputs to the angle-of-attack operating plot; anddetermining an angle-of-attack parameter corresponding to the determinedoperating point.

According to another implementation of the present disclosure, anon-transitory computer-readable storage device storing instructionsthat, when executed by a processor, cause the processor to: determine amonotonic portion of a look-up curve of an angle-of-attack operatingplot; during flight, receive from an accelerometer disposed on theunpowered vehicle, first and second accelerometer outputs, wherein thefirst and second accelerometer outputs correspond to body-fixed loadfactor measurements, respectively; determine an operating point on themonotonic portion by applying a quotient of the first and secondaccelerometer outputs to the angle-of-attack operating (look-up) plot;and determine an angle-of-attack parameter corresponding to thedetermined operating point.

The above-referenced summary section is provided to introduce aselection of concepts in a simplified form that are further describedbelow in the detailed description section. Additional concepts andvarious other implementations are also described in the detaileddescription. The summary is not intended to identify key {XE “Narrowingdesignation: key”} features or essential {XE “Narrowing designation:essential”} features of the claimed subject matter, nor is it intendedto be used to limit the scope of the claimed subject matter, nor is itintended to limit the number of inventions described herein.Furthermore, the claimed subject matter is not limited toimplementations that solve any or all {XE “Narrowing designation: all”}disadvantages noted in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present technique(s) will be described further, by way of example,with reference to embodiments thereof as illustrated in the accompanyingdrawings. It should be understood, however, that the accompanyingdrawings illustrate only the various implementations described hereinand are not meant to limit the scope of various techniques, methods,systems, or apparatuses described herein.

FIG. 1 illustrates a side view of a vehicle in accordance withimplementations of various techniques described herein.

FIG. 2 illustrates a graphical representation in accordance withimplementations of various techniques described herein.

FIG. 3 illustrates a graphical representation in accordance withimplementations of various techniques described herein.

FIG. 4 illustrates a graphical representation in accordance withimplementations of various techniques described herein.

FIG. 5 illustrates a graphical representation in accordance withimplementations of various techniques described herein.

FIG. 6 illustrates a graphical representation in accordance withimplementations of various techniques described herein.

FIG. 7 illustrates a graphical representation in accordance withimplementations of various techniques described herein.

FIG. 8 illustrates a graphical representation in accordance withimplementations of various techniques described herein.

FIG. 9 illustrates a graphical representation in accordance withimplementations of various techniques described herein.

FIG. 10 illustrates a graphical representation in accordance withimplementations of various techniques described herein.

FIG. 11 illustrates a perspective view of a tail rotor system inaccordance with implementations of various techniques described herein.

FIG. 12 is a particular illustrative aspect of methods in accordancewith implementations of various techniques described herein.

FIG. 13 is a block diagram of a computer system in accordance withimplementations of various techniques described herein.

Reference is made in the following detailed description to accompanyingdrawings, which form a part hereof, wherein like numerals may designatelike parts throughout that are corresponding and/or analogous. It willbe appreciated that the figures have not necessarily been drawn toscale, such as for simplicity and/or clarity of illustration. Forexample, dimensions of some aspects may be exaggerated relative toothers. Further, it is to be understood that other embodiments may beutilized. Furthermore, structural and/or other changes may be madewithout departing from claimed subject matter. References throughoutthis specification to “claimed subject matter” refer to subject matterintended to be covered by one or more claims, or any portion thereof,and are not necessarily intended to refer to a complete claim set, to aparticular combination of claim sets (e.g., method claims, apparatusclaims, etc.), or to a particular claim. It should also be noted thatdirections and/or references, for example, such as up, down, top,bottom, and so on, may be used to facilitate discussion of drawings andare not intended to restrict application of claimed subject matter.Therefore, the following detailed description is not to be taken tolimit claimed subject matter and/or equivalents.

DETAILED DESCRIPTION

Advantageously, systems and methods of the present disclosure allow forthe determination of an aerodynamic angle-of-attack (AOA) parameter(corresponding to a particular AOA orientation angle) without the use ofa pitot-static system including pitot-static probes (e.g., tubes, cones,vanes, etc.) having relatively bulky and/or heavy sensors. In addition,in contrast to conventional methods, because such probes are notrequired for measurement, estimation, and/or computer process,advantageously, the angle-of-attack for a gliding vehicle (i.e., anunpowered vehicle) can be determined directly with the utilization of aflight computer system and an accelerometer disposed on the glidingvehicle. In example implementations, gliding vehicles include, but arenot limited to, sailplanes, meteorological or battle damage assessmentgliders, gliding submunitions, model airplanes, or any similar flightvehicle not under direct power (e.g., a general aviation aircraftgliding with power off/engine out).

As a further advantage, in certain inventive aspects, the presentdisclosure allows for the capacity of a flight computer system togenerate a flight profile of the unpowered vehicle. Also, in certaininventive aspects, the present disclosure allows for the capacity of aflight computer system (utilizing a closed-loop control system) todetermine and correct (i.e., adjust) an AOA orientation of the unpoweredvehicle to an AOA orientation having the most advantageous lift-to-drag(i.e., lift-to-drag ratio, L/D) for maximum distance coverage.

FIG. 1 illustrates a side view of an unpowered vehicle 100 (e.g., smallglider, vehicle) during flight according to one implementation. Asshown, the unpowered vehicle 100 may travel along a velocity vector 110.As the unpowered vehicle 100 is traveling, various force vectors areshown to be enacted. These force vectors include: a normal force 120(due to pressure on the surface of the vehicle 100), a lift force 130, adrag force 140, an axial force 150, and weight. As shown in FIG. 1, incontrast to the normal force and axial force vectors (which are“body-fixed”), lift and drag force vectors are not “body-fixed” and arenormal and parallel, respectively, to the velocity vector 110. Moreover,X and Z-directions represent X and Z-body-axes of a body-axes coordinatesystem.

As further illustrated, according to a short-period pitch oscillation,when the vehicle 100 points to a particular direction of flight, theforce vectors may be expressed with respect to the incidence angle (α).Utilizing these applied forces, an accelerometer 115 may be used duringflight to measure first and second body-fixed load factor components(N_(X) and N_(Z)) (i.e., first and second body-fixed load factormeasurements, first and second body-axes load factor measurements). Incertain implementations, the accelerometer 115 may be located on thevehicle 100 at the center of gravity (CG) of the vehicle 100 or may bemathematically-corrected to the center of gravity of the vehicle 100.

As an example, the first body-fixed load factor component, N_(X) isexpressed as a quotient of a magnitude of axial force and weight, whilethe second body-fixed load factor component, N_(Z) is expressed as aquotient of a magnitude of normal force and weight. Moreover, asutilized in the inventive systems and methods (as described herein), thequotient of the first and second body-fixed load factor components maybe substantially equivalent to a quotient of a particular first andsecond body-fixed coefficients (C_(X) and C_(Z)) (as described in belowparagraphs).

${Hence},{{\frac{Nx}{Nz} = \frac{Cx}{Cz}}.}$

Advantageously, in certain implementations, this relationship isutilized in the inventive systems and methods as described herein.

In some implementations, a desired flight profile for the vehicle 100may include settings for the vehicle 100 to operate at angle-of-attackorientation allowing for the greatest lift-to-draft (L/D) for maximumdistance coverage. The LID term L/D ratio) may be computed for aparticular airspeed by measuring the lift generated in comparison withthe drag at that speed. For calculation purposes, the lift-to-draftratio may be determined by dividing the lift coefficient C_(L) by thedrag coefficient C_(D).

For the following graphical representations (FIGS. 2-11) of the systemsand methods described herein, an aircraft may dispense the vehicle 100(e.g., a small glider) for damage assessment. In other cases, thevehicle 100 may perform weather measurements, various militaryoperations (including weapons deployment), etc. In the example, thevehicle 100 includes a weight of 1-pound, a wingspan of 16-inch, and a2-inch wing-chord. For each of the graphical representations (200-1100),the Y-component ranges may vary depending upon weight, wingspan, andwing-chord characteristics of the particular vehicle.

In FIG. 2, graph 200 illustrates estimated drag coefficient curves forthree elevator deflection settings (de): −5, 0, and 5. As shown, graph200 includes an expected range for drag, as represented as dragcoefficient values C_(D) (from 0 to 0.35) for the vehicle 100 (on theY-axis) 210, as a function of a range of angle-of-attack directions(from −5° to 20°) (on the X-axis) 220. In certain implementations, thedrag coefficient C_(D) is a dimensionless quantity that may be used toquantify the drag or resistance of the vehicle 100 in a fluidenvironment, such as air or water.

In FIG. 3, graph 300 illustrates estimated lift coefficient curves forthe three elevator deflection settings (de): −5, 0, and 5. As shown,graph 300 includes an expected range for lift, as represented as liftcoefficient values C_(L) (from −2 to 1.6), for the vehicle 100 (on theY-axis) 310, as a function of the range of angle-of-attack directions(from −5° to 20°) (on the X-axis) 320. In certain implementations, thelift coefficient C_(L) is a dimensionless quantity that may be used toquantify the lift generated by the vehicle 100 to the fluid densityaround the vehicle 100, the fluid velocity, and an associated foil chordof the vehicle 100.

In certain implementations, the lift and drag coefficient values areaerodynamic data characteristics (i.e., first and second aerodynamicdata values) that may be obtained by estimating the range of thebody-fixed accelerations C_(X)/C_(Z) (as described in below paragraphs)for the vehicle 100 or by measuring wind tunnel data with respect to thevehicle 100.

FIGS. 4 and 5 illustrate the drag coefficient values C_(D) and liftcoefficient values C_(L) transformed to body-fixed coefficients: bodyX-force coefficient (i.e., first body-fixed coefficient) and bodyZ-force coefficient C_(Z) (i.e., second body-fixed coefficient),respectively. In one implementation, the first and second body-fixedcoefficients C_(X) and C_(Z) may be determined through computation ofthe following equations:

C _(X) =−C _(D) cos α+C _(L) sin α

C_(Z) =−C _(L) cos α−C_(D) sin α

In FIG. 4, graph 400 illustrates the body X-force coefficient (i.e., thefirst body-fixed coefficient) for the three elevator deflection settings(de): −5, 0, and 5. As shown, graph 400 includes a range of body X-forcecoefficients (from −0.05 to 0.2) (on the Y-axis) 410 as a function ofthe range of angle-of-attack directions (from −° to 20°) (on the X-axis)420.

In FIG. 5, graph 500 illustrates the body Z-force coefficient (i.e., thesecond body-fixed coefficient) for the three elevator deflectionsettings (de): −5, 0, and 5. As shown, graph 500 includes a range ofbody Z-force coefficients (from −1.6 to 0.2) (on the Y-axis) 510 as afunction of the range of angle-of-attack directions (from −5° to 20°)(on the X-axis) 520.

In FIG. 6, graph 600 illustrates the C_(X)/C_(Z) ratio for the threeelevator deflection settings (de): −5, 0, and 5. As shown, graph 600includes the C_(X)/C_(Z) ratio (from −8 to 4) (on the Y-axis) 610 as afunction of the range of angle-of-attack directions (from −5° to 20°)(on the X-axis) 620. Notably, a collapse may be seen on the graphcurvature (C_(X)/C_(Z) ratio plot points over a range of usableangle-of-attack) for the “0” elevator deflection setting.

In FIG. 7, graph 700 illustrates a portion of the C_(X)/C_(Z) ratio forthe “0” elevator deflection setting (de=0) from FIG. 6. As shown, graph700 (i.e., an angle-of-attack operating plot, angle-of-attack operatingmap, angle-of-attack look-up plot) includes the C_(X)/C_(Z) ratio (from−0.5 to 3/5) (on the Y-axis) 710 as a function of the range ofangle-of-attack directions (from −5° to 20°) (on the X-axis) 720.Notably, a monotonic portion 740 (of the C_(X)/C_(Z) ratio as a functionof the range of angle-of-attack directions) of a C_(X)/C_(Z) look-upcurve 730 (i.e., a monotonic curve, body-fixed accelerations curve)(e.g., a portion of the curvature 730 that does not increase) can serveas a look-up curve (i.e., a look-up table) or be applied incurve-fitting for a range (i.e., a plurality) of prospective (i.e.,possible, useful) angle of attack operating points. In oneimplementation, a particular operating point on the monotonic portionmay be determined by applying a quotient of the first and secondaccelerometer outputs (i.e., N_(X)/N_(Z)) to the angle-of-attackoperating (look-up) plot 700. For instance, this may be applied bymatching a quotient of the first and second accelerometer outputs(N_(X)/N_(Z)) to a substantially equivalent body-fixed acceleration(C_(X)/C_(Z)), where the body-fixed acceleration (C_(X)/C_(Z)) maycorrespond to a particular quotient of a particular first and secondbody-fixed coefficients (C_(X), C_(Z)). Upon matching

${\frac{Nx}{Nz} = \frac{Cx}{Cz}},$

a computer system (e.g., such as any of the computers in flight computersystem 1300) may determine an angle-of-attack parameter that correspondsto the determined operating point.

Accordingly, in the example methods, after the drag coefficient valuesC_(D) and the lift coefficient values C_(L) are transformed intorespective components of the first and second body-fixed coefficientsC_(X) and C_(Z), a C_(X)/C_(Z) ratio (i.e., a body-fixed acceleration)may be used to establish the monotonic portion 740 for angle-of-attacklook-up. Moreover, measured accelerometer components N_(X) and N_(Z) maybe divided and matched on a monotonic portion of a lookup curve on aplot comparing body-fixed accelerations to prospective AOA parameters.Further, an operating point that aligns to the Y-axis may be used todetermine where on the X-axis (of prospective AOA parameters) alignmenttakes place.

In FIG. 8, graph 800 illustrates a lift-to-drag ratio C_(L)/C_(D) forthe three elevator deflection settings (de): −5, 0, and 5. As shown,graph 800 includes the lift-to-drag ratio C_(L)/C_(D) (from −5 to 15)(on the Y-axis) 810 as a function of the range of angle-of-attackdirections (from −5° to 20°) (on the X-axis) 820. Notably, provided onlift-to-drag ratio C_(L)/C_(D) curves 830, graph 800 depicts therespective operating points 834 (for the three elevator deflectionsettings) and the corresponding AOA parameter 836 for selection of anideal angle-of-attack operating point, if an optimal lift-to-drag ratiois to be prioritized. In such an example, the angle-of-attack parametercorresponds to a lift-to-drag-optimized angle-of-attack.

In FIG. 9, graph 900 illustrates a lift-to-drag C_(L) ^(3/2)/C_(D) ratio(i.e., a second lift-to-drag ratio) for the three elevator deflectionsettings (de): −5, 0, and 5. As shown, graph 900 includes the secondlift-to-drag C_(L) ^(3/2)/C_(D) ratio (from 0 to 154) (on the Y-axis)910 as a function of the range of angle-of-attack directions (from −5°to 20°) (on the X-axis) 920. Notably, graph 900 depicts the respectiveoperating points 934 (for the provided deflection settings) and thecorresponding AOA parameter 936 selection if a minimum power point(i.e., a minimum sink rate) is to be prioritized. In such an example,the angle-of-attack parameter corresponds to a minimum-sinkrate-optimized angle of attack. In other examples, a combination of twocriteria (lift-to-drag and minimum sink-rate) may be used in evaluationfor an optimal AOA.

FIG. 10 illustrates time history results of a six-degree-of-freedomflight simulation of the vehicle 100 capturing 7° angle-of-attack tooperate near maximum lift-to-drag. In FIG. 10A, graph 1000 includesangle of attack (from 3.5° to 7°) (on the Y-axis) 1010 as a function oftime (0-200 seconds) (on the X-axis) 1020. The angle-of-attackcomparison shows the comparison of a simulation vehicle angle-of-attack(as shown as the solid line in FIG. 10) with the estimatedangle-of-attack (as shown as the dashed-line in FIG. 10), according toexamples as described herein. The estimated angle-of-attack shown is theresult of using the ratio N_(X)/N_(Z) from the body-fixed accelerations(i.e., C_(X)/C_(Z)) as input to a table look-up of the monotonic portionof the body-fixed accelerations (i.e., C_(X)/C_(Z)) curve as discussedwith reference to FIG. 7 above. As an additional graph for referencepurposes, in FIG. 11, graph 1100 illustrates Lift/Drag ratio (from0-12.2) (on the Y-axis) 1110 as a function of time (0-200 seconds) (onthe X-axis) 1120.

Referring to FIG. 12, a method 1200 (e.g., implemented as an AOAoptimization program) for determining angle-of-attack for an unpoweredvehicle 100 applicable for the flight computer system 1300 (as describedwith reference to FIG. 13) is shown.

At block 1210, the method 1200 includes determining a monotonic portionof a look-up curve of an angle-of-attack operating plot. For example, incertain implementations, with reference to FIG. 7, a monotonic portion740 of a look-up curve 730 (i.e., a monotonic curve, table look-up;body-fixed accelerations curve) of an angle-of-attack operating plot 700may be determined (i.e., identified, generated). In someimplementations, a monotonic portion 740 of a look-up curve 730 of anangle-of-attack operating plot 700, may be generated prior to animplementation of the method 1200 in any computer either networked to oroutside of the computer system 1300, and in other implementations, amonotonic portion 740 of a look-up curve 730 of an angle-of-attackoperating plot 700, may be performed concurrently (i.e., in real-time)in any computer networked to the computer system 1300 as part of themethod 1200.

As discussed with reference to FIGS. 2-7 (in above paragraphs),determining a monotonic portion of a look-up curve of an angle-of-attackoperating plot may include the following steps: (1) obtainingpluralities of first and second aerodynamic data characteristics (i.e.,values, metrics) as respective functions of a range of angle-of-attackdirections; (2) computing, by a processor (e.g., a microcontroller,onboard flight control processing device), pluralities of first andsecond body-fixed coefficients (C_(X) and C_(Z)) as the respectivefunctions of the range of angle-of-attack directions; (3) determining,by the processor, a plurality of body-fixed accelerations (i.e.,C_(X)/C_(Z)) as a function of a prospective range of the range ofangle-of-attack directions based on respective pluralities of quotientsof the first and second body-fixed coefficients as the respectivefunctions of the range of angle-of-attack directions, where thedetermined plurality of body-fixed accelerations (i.e., C_(X)/C_(Z)) asa function of a prospective range of the range of angle-of-attackdirections corresponds to the look-up curve of the angle-of-attackoperating plot; and (4) determining the monotonic portion based on afiltering, by the processor, of the look-up curve.

At block 1220, the method 1200 includes during flight, determining, byan accelerometer disposed on the unpowered vehicle, first and secondaccelerometer outputs, where the first and second accelerometer outputscorrespond to first and second body-fixed load factor measurements,respectively. For example, as described with reference to FIG. 1, firstand second body-fixed load factor measurements (N_(X) and N_(Z)) can bemeasured with the aid of an accelerometer 115 disposed on the unpoweredvehicle 100.

At block 1230, the method 1200 includes determining an operating pointon the monotonic portion by applying a quotient of the first and secondaccelerometer outputs to the angle-of-attack operating plot. Forexample, as described with reference to FIGS. 1 and 7, a particularoperating point on the monotonic portion 740 may be determined byapplying a quotient of the first and second accelerometer outputs (i.e.,N_(X)/N_(Z)) to the angle-of-attack operating plot 700.

In one implementation, step 1230 is carried out by matching a quotientof the first and second accelerometer outputs (N_(X)/N_(Z)) to asubstantially equivalent body-fixed acceleration (C_(X)/C_(Z)), wherethe body-fixed acceleration (C_(X)/C_(Z)) may correspond to a particularquotient of a particular first and second body-fixed coefficients(C_(X), C_(Z)).

At block 1240, the method 1200 includes determining an angle-of-attackparameter corresponding to the determined operating point. For example,as discussed with reference with FIG. 7, upon matching

${\frac{Nx}{Nz} = \frac{Cx}{Cz}},$

a computer system (e.g., such as any computer of computer system 1300)may determine an angle-of-attack parameter that corresponds to thedetermined operating point.

The method 1200 include further steps such as: in response todetermining the angle-of-attack parameter at least one of: (1)generating, at least partially by a flight computer system, a flightprofile of the unpowered vehicle; and (2) adjusting (i.e., correcting),at least partially by the flight computer system (and a closed-loopsystem), an angle-of-attack setting of the unpowered vehicle based onthe angle-of-attack parameter.

Advantageously, for instance, the computer system 1300 (as describedwith reference to FIG. 13) may generate a flight profile for the vehicle100. The flight profile may be based on the determined AOA parameter andmay include: an optimal AOA for lift-to-drag-optimized angle-of-attack,an optimal AOA for minimum-sink rate-optimized angle of attack, or acombination thereof. The flight computer system may further adjust(correct for) an angle-of-attack setting of the unpowered vehicle 100based on the determined angle-of-attack parameter such that anassociated closed-loop control system may automatically correct theunpowered vehicle in real-time. In addition, the determined AOAparameter may also be used in AOA feedback for stability augmentation(i.e., to improve static stability) in a linear range and also may beused as a stall warning. Accordingly, an operator (e.g., pilot,engineer, aerodynamicist, or flight computer) may evaluate that adetermined AOA parameter corresponds to a determined operating point ina sub-optimal region, and thus, the operator may take further actions(such as determining an improved operating point) to bring the AOA ofthe unpowered vehicle 100 “back” to the optimal AOA.

FIG. 13 is a diagram depicting the computer system 1300 (e.g., networkedcomputer system and/or server) for the example unpowered vehicle 100 (asdescribed in FIG. 1), according to one implementation. FIG. 13illustrates example hardware components in the computer system 1300 thatmay be used to determine and/or correct (i.e., adjust) anangle-of-attack parameter (i.e., orientation) for the vehicle 100. Thecomputer system 1300 includes a computer 1310 (e.g., computer, flightcomputer system, flight controls and avionics computer system), whichmay be implemented as a server or a multi-use computer that is coupledvia a network 1340 to one or more networked (client) computers 1320,1330. The method 1200 may be stored as program code (i.e., AOAoptimization program 1324) in memory that may be performed by thecomputer 1310, the computers 1320, 1330, other networked electronicdevices (not shown) or a combination thereof. In some implementations,the AOA optimization program 1324 may read input data (e.g., receivedmeasurements from the accelerometer 115 and operating plot data ofrespective angle-of-attack operating plots 1317) and provide controlledoutput data to various connected computer systems including anassociated closed-loop control system. In certain implementations, eachof the computers 1310, 1320, 1330 may be any type of computer, computersystem, or other programmable electronic device. Further, each of thecomputers 1310, 1320, 1330 may be implemented using one or morenetworked (e.g., wirelessly networked) computers, e.g., in a cluster orother distributed computing system. Each of the computers 1310, 1320,1330 may be implemented within a single computer or programmableelectronic device, e.g., an aircraft flight control computer, aground-based flight control system, a flight monitoring terminal, alaptop computer, a hand-held computer, phone, tablet, etc. In oneexample, the computer system 1310 may be an onboard flight controlcomputer (e.g., that is configured to receive accelerometer data fromthe vehicle 100) on a dispensing aircraft. In such an example, thecomputer 1320 may be located on the vehicle 100 (e.g., to transmit datafrom the accelerometer 115 located on the vehicle 100), and the computer1330 (e.g., that is also configured to receive the accelerometer datafrom the vehicle 100) may be a part of the computer system 1300 at aground location monitoring the aircraft and the vehicle 100.

Advantageously, in example implementations, one or more of the computers1310, 1320, and 1330 of the flight computer system 1300 may generate aflight profile of the unpowered vehicle 100 and/or adjust (in someinstances, automatically) an angle-of-attack configuration (i.e.,setting) of the unpowered vehicle 100 based on a determinedangle-of-attack parameter of the unpowered vehicle 100.

In one implementation, the computer 1300 includes a central processingunit (CPU) 1312 having at least one hardware-based processor coupled toa memory 1314. The memory 1314 may represent random access memory (RAM)devices of main storage of the computer 1310, supplemental levels ofmemory (e.g., cache memories, non-volatile or backup memories (e.g.,programmable or flash memories)), read-only memories, or combinationsthereof. In addition to the memory 1314, the computer system 1300 mayinclude other memory located elsewhere in the computer 1310, such ascache memory in the CPU 1312, as well as any storage capacity used as avirtual memory (e.g., as stored on a storage device 1316 or on anothercomputer coupled to the computer 1310). The memory 1314 may include anAOA optimization program 1324 to determine an AOA parameter of thevehicle 100, and the storage device 1316 may include monotonic portionson respective angle-of-attack operating plots 1317 for a variety ofdifferent vehicles (to be utilized with the AOA optimization program1324) (as described in greater detail with reference to FIGS. 7, 12, and13). In certain implementations, the AOA optimization program 1324 maydetermine optimal AOA parameters and adjust (e.g., automatically in someinstances) AOA configurations based on the optimal AOA parametersutilizing the monotonic portions (e.g., monotonic portion 740) of thestored AOA operating plots 1317.

In FIG. 13, the storage device 1316 is shown to include the stored(monotonic portions on respective) angle-of-attack operating plots 1317.In other alternative implementations, (the monotonic portions onrespective) the angle-of-attack operating plots 1317 may be stored inthe memory 1314, in memory in the computers 1320, 1330, or in any otherconnected or networked memory storages devices. In some implementations,a monotonic portion for a particular angle-of-attack operating plot maybe determined in real-time and concurrent with the AOA optimizationoperation 1324. In other implementations, a monotonic portion for aparticular angle-of-attack operating plot may be determined prior to theAOA optimization operation 1324.

The computer 1310 may further be configured to communicate informationexternally. To interface with a user or operator (e.g., aerodynamicist,engineer), the computer 1310 may include a user interface (I/F) 1318incorporating one or more user input devices (e.g., a keyboard, a mouse,a touchpad, and/or a microphone, among others) and a display (e.g., amonitor, a liquid crystal display (LCD) panel, light emitting diode(LED), display panel, and/or a speaker, among others). In otherexamples, user input may be received via another computer or terminal.Furthermore, the computer 1310 may include a network interface (I/F)1320 which may be coupled to one or more networks 1340 (e.g., a wirelessnetwork) to enable communication of information with other computers andelectronic devices. The computer 1310 may include analog and/or digitalinterfaces between the CPU 1312 and each of the components 1314, 1316,1318 and 1320. Further, other non-limiting hardware environments may beused within the context of example implementations.

The computer 1310 may operate under the control of an operating system1326 and may execute or otherwise rely upon various computer softwareapplications, components, programs, objects, modules, data structures,etc. (such as the AOA optimization program 1324 and related software).The operating system 1326 may be stored in the memory 1314. Operatingsystems include, but are not limited to, UNIX® (a registered trademarkof The Open Group), Linux® (a registered trademark of Linus Torvalds),Windows® (a registered trademark of Microsoft Corporation, Redmond,Wash., United States), AIX® (a registered trademark of InternationalBusiness Machines (IBM) Corp., Armonk, N.Y., United States) i5/OS® (aregistered trademark of IBM Corp.), and others as will occur to those ofskill in the art. The operating system 1326 and the AOA optimizationprogram 1324 in the example of FIG. 13 are shown in the memory 1314, butcomponents of the aforementioned software may also, or in addition, bestored at non-volatile memory (e.g., on storage device 1316 (datastorage) and/or the non-volatile memory (not shown). Moreover, variousapplications, components, programs, objects, modules, etc. may alsoexecute on one or more processors in another computer coupled to thecomputer 1310 via the network 1340 (e.g., in a distributed orclient-server computing environment) where the processing to implementthe functions of a computer program may be allocated to multiplecomputers 1320, 1330 over the network 1340.

Aspects of the present disclosure may be incorporated in a system, amethod, and/or a computer program product. The computer program productmay include a computer-readable storage medium (or media) havingcomputer-readable program instructions thereon for causing a processorto carry out aspects of the present disclosure. The computer-readablestorage medium can be a tangible device that can retain and storeinstructions for use by an instruction execution device. Thecomputer-readable storage medium may be, for example, but is not limitedto, an electronic storage device, a magnetic storage device, an opticalstorage device, an electromagnetic storage device, a semiconductorstorage device, or any suitable combination of the foregoing. Anon-exhaustive list of more specific examples of the computer-readablestorage medium includes the following: a portable computer diskette, ahard disk, a random access memory (RAM), a read-only memory (ROM), anerasable programmable read-only memory (EPROM or Flash memory), a staticrandom access memory (SRAM), a portable compact disc read-only memory(CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk,a mechanically encoded device such as punch-cards or raised structuresin a groove having instructions recorded thereon, and any suitablecombination of the foregoing. A computer-readable storage medium, asused herein, is not to be construed as being transitory signals per se,such as radio waves or other freely propagating electromagnetic waves,electromagnetic waves propagating through a waveguide or othertransmission media (e.g., light pulses passing through a fiber-opticcable), or electrical signals transmitted through a wire. For example,the memory 1314, the storage device 1316, or both, may include tangible,non-transitory computer-readable media or storage devices.

Computer-readable program instructions described herein can bedownloaded to respective computing/processing devices from acomputer-readable storage medium or to an external computer or externalstorage device via a network, for example, the Internet, a local areanetwork, a wide area network and/or a wireless network. The network maycomprise copper transmission cables, optical transmission fibers,wireless transmission, routers, firewalls, switches, gateway computersand/or edge servers. A network adapter card or network interface in eachcomputing/processing device receives computer-readable programinstructions from the network and forwards the computer-readable programinstructions for storage in a computer-readable storage medium withinthe respective computing/processing device.

Computer-readable program instructions for carrying out operations ofthe present disclosure may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andprocedural programming languages, such as the “C” programming languageor similar programming languages. The computer-readable programinstructions may execute entirely on the user's computer, partly on theuser's computer, as a stand-alone software package, partly on the user'scomputer and partly on a remote computer or entirely on the remotecomputer or server. In the latter scenario, the remote computer may beconnected to the user's computer through any type of network, includinga local area network (LAN) or a wide area network (WAN), or theconnection may be made to an external computer (for example, through theInternet using an Internet Service Provider). In some implementations,electronic circuitry including, for example, programmable logiccircuitry, field-programmable gate arrays (FPGA), or programmable logicarrays (PLA) may execute the computer-readable program instructions byutilizing state information of the computer-readable programinstructions to personalize the electronic circuitry, in order toperform aspects of the present disclosure.

Aspects of the present disclosure are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of thedisclosure. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer-readable program instructions.

These computer-readable program instructions may be provided to aprocessor of a general-purpose computer, a special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus. The machine is anexample of means for implementing the functions/acts specified in theflowchart and/or block diagrams. The computer-readable programinstructions may also be stored in a computer-readable storage mediumthat can direct a computer, a programmable data processing apparatus,and/or other devices to function in a particular manner, such that thecomputer-readable storage medium having instructions stored thereincomprises an article of manufacture including instructions whichimplement aspects of the functions/acts specified in the flowchartand/or block diagrams.

The computer-readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to perform a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagrams.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousimplementations of the present disclosure. In this regard, each block inthe flowchart or block diagrams may represent a module, segment, orportion of instructions, which comprises one or more executableinstructions for implementing the specified logical function(s). In somealternative implementations, the functions noted in a block in a diagrammay occur out of the order noted in the figures. For example, two blocksshown in succession may be executed substantially concurrently, or theblocks may sometimes be executed in the reverse order, depending uponthe functionality involved. It will also be noted that each block of theblock diagrams and/or flowcharts, and combinations of blocks in theblock diagrams and/or flowcharts, can be implemented by special purposehardware-based systems that perform the specified functions or acts orcarry out combinations of special purpose hardware and computerinstructions.

In the following description, numerous specific details are set forth toprovide a thorough understanding of the disclosed concepts, which may bepracticed without some or all of these particulars. In other instances,details of known devices and/or processes have been omitted to avoidunnecessarily obscuring the disclosure. While some concepts will bedescribed in conjunction with specific examples, it will be understoodthat these examples are not intended to be limiting.

Unless otherwise indicated, the terms “first”, “second”, etc. are usedherein merely as labels, and are not intended to impose ordinal,positional, or hierarchical requirements on the items to which theseterms refer. Moreover, reference to, e.g., a “second” item does notrequire or preclude the existence of, e.g., a “first” or lower-numbereditem, and/or, e.g., a “third” or higher-numbered item.

Reference herein to “one example” means that one or more feature,structure, or characteristic described in connection with the example isincluded in at least one implementation. The phrase “one example” invarious places in the specification may or may not be referring to thesame example.

Illustrative, non-exhaustive examples, which may or may not be claimed,of the subject matter according to the present disclosure are providedbelow. Different examples of the device(s) and method(s) disclosedherein include a variety of components, features, and functionalities.It should be understood that the various examples of the device(s) andmethod(s) disclosed herein may include any of the components, features,and functionalities of any of the other examples of the device(s) andmethod(s) disclosed herein in any combination, and all of suchpossibilities are intended to be within the scope of the presentdisclosure. Many modifications of examples set forth herein will come tomind to one skilled in the art to which the present disclosure pertainshaving the benefit of the teachings presented in the foregoingdescriptions and the associated drawings.

Therefore, it is to be understood that the present disclosure is not tobe limited to the specific examples illustrated and that modificationsand other examples are intended to be included within the scope of theappended claims. Moreover, although the foregoing description and theassociated drawings describe examples of the present disclosure in thecontext of certain illustrative combinations of elements and/orfunctions, it should be appreciated that different combinations ofelements and/or functions may be provided by alternative implementationswithout departing from the scope of the appended claims. Accordingly,parenthetical reference numerals in the appended claims are presentedfor illustrative purposes only and are not intended to limit the scopeof the claimed subject matter to the specific examples provided in thepresent disclosure.

What is claimed is:
 1. A method for determining an angle-of-attack foran unpowered vehicle, comprising: determining a monotonic portion of alook-up curve of an angle-of-attack operating plot; during flight,determining, by an accelerometer disposed on the unpowered vehicle,first and second accelerometer outputs, wherein the first and secondaccelerometer outputs correspond to first and second body-fixed loadfactors, respectively; determining an operating point on the monotonicportion by applying a quotient of the first and second accelerometeroutputs to the angle-of-attack operating plot; and determining anangle-of-attack parameter corresponding to the determined operatingpoint.
 2. The method of claim 1, further comprising, in response todetermining the angle-of-attack parameter, at least one of: generating,at least partially by a flight computer system, a flight profile of theunpowered vehicle; and adjusting, at least partially by the flightcomputer system, an angle-of-attack setting of the unpowered vehiclebased on the angle-of-attack parameter.
 3. The method of claim 1,wherein determining the operating point on the monotonic curve portionby applying the quotient of the first and second accelerometer outputsto the angle-of-attack operating plot comprises: matching a quotient ofthe first and second accelerometer outputs to a substantially equivalentbody-fixed acceleration, wherein the body-fixed acceleration correspondsto a particular quotient of a particular first and second body-fixedcoefficients.
 4. The method of claim 3, wherein the particular quotientof the first and second body-fixed coefficient corresponds to aparticular respective first and second aerodynamic data characteristic.5. The method of claim 4, wherein the particular respective first andsecond aerodynamic data characteristic corresponds to a particularrespective lift coefficient metric and drag coefficient metric.
 6. Themethod of claim 1, wherein the monotonic curve portion corresponds to aplurality of body-fixed accelerations as a function of a plurality ofangle-of-attack parameters.
 7. The method of claim 6, wherein theplurality of angle-of-attack parameters corresponds to a respectiverange of prospective angle-of-attack directions.
 8. The method of claim7, wherein the angle-of-attack parameter of the plurality ofangle-of-attack parameters corresponds to one direction of the range ofthe prospective angle-of-attack directions, and wherein theangle-of-attack parameter corresponds to a lift-to-drag-optimizedangle-of-attack, a minimum-sink rate-optimized angle of attack, or acombination thereof.
 9. The method of claim 6, wherein the plurality ofbody-fixed accelerations corresponds to a quotient of the pluralities offirst and second body-fixed coefficients.
 10. The method of claim 9,wherein the plurality of a first body-fixed coefficient is based on acorresponding plurality of a first aerodynamic data characteristic and arange of angle-of-attack directions.
 11. The method of claim 10, whereinthe plurality of a first aerodynamic data characteristic comprises aplurality of lift coefficient metrics.
 12. The method of claim 9,wherein the plurality of a second body-fixed coefficient is based on acorresponding plurality of a second aerodynamic data characteristic anda range of angle-of-attack directions.
 13. The method of claim 12,wherein the plurality of a second aerodynamic data characteristiccomprises a plurality of drag coefficient metrics.
 14. The method ofclaim 1, wherein the operating point corresponds to a particularbody-fixed acceleration as function of a corresponding particularangle-of-attack parameter.
 15. The method of claim 1, wherein the firstbody-fixed load factor measurement corresponds to a quotient of amagnitude of axial force and weight, and wherein the second body-fixedload factor measurement corresponds to a quotient of a magnitude ofnormal force and weight.
 16. The method of claim 1, wherein determiningthe monotonic portion of the look-up curve of the angle-of-attackoperating plot comprises: obtaining pluralities of first and secondaerodynamic data characteristics as respective functions of a range ofangle-of-attack directions; computing, by a processor, pluralities offirst and second body-fixed coefficients as the respective functions ofthe range of angle-of-attack directions; determining, by the processor,a plurality of body-fixed accelerations as a function of a prospectiverange of the range of angle-of-attack directions based on respectivepluralities of quotients of the first and second body-fixed coefficientsas the respective functions of the range of angle-of-attack directions,wherein the determined plurality of body-fixed accelerations as afunction of a prospective range of the range of angle-of-attackdirections corresponds to the look-up curve of the angle-of-attackoperating plot; and determining the monotonic portion based on afiltering, by the processor, of the look-up curve.
 17. The method ofclaim 16, wherein the pluralities of first and second aerodynamic datacharacteristics are obtained by estimating the range of the body-fixedaccelerations for the vehicle or by measuring wind tunnel data withrespect to the vehicle.
 18. The method of claim 16, wherein a graphcomparing a range of body-fixed accelerations as a function of theprospective range of the range of angle-of-attack directions correspondsto the angle-of-attack operating plot.
 19. A flight computer systemcomprising: a processor; and a memory accessible to the processor, thememory storing instructions that are executable by the processor toperform operations comprising: determining a monotonic portion of alook-up curve of an angle-of-attack operating plot; during flight,receiving from an accelerometer disposed on the unpowered vehicle, firstand second accelerometer outputs, wherein the first and secondaccelerometer outputs correspond to first and second body-fixed loadfactor measurements, respectively; determining an operating point on themonotonic portion by applying a quotient of the first and secondaccelerometer outputs to the angle-of-attack operating plot; anddetermining an angle-of-attack parameter corresponding to the determinedoperating point.
 20. A non-transitory computer-readable storage devicestoring instructions that, when executed by a processor, cause theprocessor to: determine a monotonic portion of a look-up curve of anangle-of-attack operating plot; during flight, receive from anaccelerometer disposed on the unpowered vehicle, first and secondaccelerometer outputs, wherein the first and second accelerometeroutputs correspond to first and second body-fixed load factormeasurements, respectively; determine an operating point on themonotonic portion by applying a quotient of the first and secondaccelerometer outputs to the angle-of-attack operating plot; anddetermine an angle-of-attack parameter corresponding to the determinedoperating point.